A series of Mn-Zn ferrite particles was prepared by a template-assisted sol-gel method and calcined at 773, 973 and 1173 K in air, nitrogen and nitrogen after precalcination at 573 K for 1h in air respectively. The effects of calcined conditions on composition, morphology and properties of Mn-Zn ferrites were investigated by XRD, TEM, VSM and impedance analyzer. It was found that Mn-Zn ferrites with pure spinel structure, uniform size and morphology were obtained only in nitrogen after precalcination at 573 K for 1h in air, which provided a new way to prepare Mn-Zn ferrite nanoparticles with spinel structure. The reaction mechanisms of the Mn-Zn ferrites in different calcined atmospheres were analyzed. The calcined temperature had a major influence on the morphology and properties of the Mn-Zn ferrite particles with spinel structure obtained; and with the increasing of the calcination temperature, the particles in size became larger, M_s increased monotonically, H_c first increased and then decreased, T_c decreased monotonically. The permittivity first increased and then decreased, and the dielectric loss showed a sharp rise after slightly reducing trend with the increasing of frequency.